PORTLAND, Maine — Portland property owners on Monday night offered mixed reviews of a plan to begin charging a new fee for impervious surfaces, intended to spread out the cost burden of looming and expensive sewer system updates.

Nearly 40 people attended a presentation Monday night of the city’s Sustainable Stormwater Funding Task Force in a first-floor City Hall conference room.

The issue is coming to a head as Portland faces approximately $170 million in sewer system updates over the next 15 years to bring what are in some places pre-Civil War era pipes and culverts up to more contemporary standards.

In more than half of the city’s aging sewer pipe network now, stormwater and sewage waste are combined into a single drainage system. During heavy rains, the stormwater drives the volume up to a level that exceeds the amount treatment facilities can handle, triggering discharges of untreated sewage and industrial waste into sensitive water bodies such as rivers, streams and Casco Bay.

Story continues below advertisement.

“A lot of people aren’t aware of that,” said Ed Suslovic, City Council member and chairman of the 18-member task force set up nearly a year ago to look into how to cover those costs. “They think, ‘It’s America, this isn’t a Third World country, when I flush my toilet it gets treated.’ Well, that’s not always the case.”

The environmental hazards resulting from the discharges have attracted scrutiny by federal and state regulators, who are mandating progress toward reducing the amount of sludge belched into the rivers and streams.

In accordance with U.S. Environmental Protection Agency demands, the city has chipped away at the problem since 1993, with more than 100 projects worth $120 million having been performed or planned. The work to date has cut annual sewer overflows from 720 million gallons in 1993 to 420 million gallons in 2010, according to the city.

The task force, set up last April by the City Council, is recommending that half of the looming $170 million in costs be raised through sewer rate increases and the other half through the impervious surface fee, which would charge based on the square footage of roofs, sidewalks, driveways and parking lots. Suslovic said the average single-family residential property has about 2,500 square feet of impervious surface.

He said the rate will be determined, in part based on the annual costs being incurred on projects. Suslovic said a current average single-family homeowner pays $422 a year in sewer fees, and that will escalate to $853 if the city makes no changes in its charging formula. But by diverting some of the cost to property owners with large amounts of impervious surfaces, he said, that increase will be slightly less, at $852.

He said two- and three-unit residential property owners would see more substantial savings with the cost shift, ranging into the hundreds of dollars.

“All the money so far, the $120 million, has been raised exclusively through the sewer fee,” Suslovic said during Monday night’s meeting. “It’s one of the reasons the sewer fee in Portland has been going up. We already have one of the highest sewer fees in the country, and it’s going to continue going up unless we do something different.”

The next phase of renovations reportedly will reduce discharges of untreated waste down to 87 million gallons annually. Suslovic said the next phase of project includes the construction of a 15 million-gallon storage facility to capture diverted stormwater temporarily until the rain events subside and the treatment plant is capable of handling the extra volume, as well as upgrades to the East End Wastewater Treatment Facility itself.

He also said the plan includes credits for property owners who implement measures to reduce stormwater runoff, as well as a cap on how much any ratepayer would pay from one year to the next. The task force’s final meeting is slated for March 20, at which time the panel hopes to complete its recommendations and forward them to the City Council.

Nearly a dozen comments or questions were offered to the task force Monday night, with some attendees asking for the new stormwater fees to be higher — to shift the repair costs off residential homeowners — while others, such as Portland Community Chamber Government Relations Consultant Chris O’Neil, called for the stormwater fees to initially be lower.

O’Neil said the Chamber’s member business leaders “value and seek to protect our environment — on that we all agree.”

But he said absorbing 50 percent of the cost burden through impervious surface fees at the onset of the plan “is too high, especially at first.”

“We think it’s too high a burden to suddenly land on one group,” O’Neil said, adding that wastewater ratepayers can “more easily” change practices to reduce their output.

O’Neil said many municipalities within 15 miles of Portland have sewer rates less than half of the city’s, already placing Portland at a competitive disadvantage attracting and retaining businesses. He said Scarborough charges less than $3 a cubic yard, for example, while Portland charges more than $8 a cubic yard.

He also reiterated calls for city leaders to engage the Maine’s congressional delegation and federal environmental regulators to seek funding help or flexibility in complying with water quality standards.

“Have we simply capitulated to the EPA? Have we ever pushed back?” O’Neil said. “There seems to be a mentality where we just rolled over and said, ‘Here’s the checkbook, take what you want.’”